The present invention relates to the selective catalytic alkylation, e.g., propylation, of phenolic compounds to produce an alkylphenolic reaction product enriched in the para-isopropyl isomer of the phenol being alkylated.
2. Description of the Prior Art
Propylated phenolic compounds such as para-isopropylphenol are useful materials in the synthesis of various products such as adhesives, agricultural chemicals and pharmaceuticals. It is known to prepare such compounds via the alkylation of phenolic compounds with such propylating agents as propylene and isopropanol, and a variety of alkylation catalysts are known to promote such a reaction. For example, U.S. Pat. No. 3,959,394; 3,439,048; 3,426,358; 3,426,082; 3,409,678; 3,382,283; 3,367,981; 3,265,742; 3,185,737; 3,133,974; 3,082,258 and 3,071,595, all disclose alkylation of phenol over a variety of catalysts such as Friedel Crafts catalysts (AlCl.sub.3, HF, BF.sub.3, etc.), zinc halides, alumina, aluminum phenoxide, alkane sulfonic acids and the like. Although many of these reactions are said to favor formation of the ortho-alkylphenols, reaction products in all instances contain at least some of the para- and meta-isomers as well.
Separation of the para-isomer of propylated phenol from mixtures containing the other isomers of this compound is not economically attractive unless the product mixture contains a relatively high concentration of the para-isomer. Accordingly, attempts have been made to alkylate phenol under conditions which selectively promote formation of the para-alkylphenol isomer. Thus, for example, Belgian Pat. No. 871,105 discloses the para-selective alkylation of phenol with olefins over strongly acid ion exchange resin catalysts, and Japanese Patent Specification 54073738 discloses alkylation of phenol with olefins over titanium and molybdenum oxides followed by isomerization to the p-isomer over H.sub.2 SO.sub.4 or silica-alumina.
Notwithstanding such efforts to maximize production of the para-isopropyl isomer during alkylation of phenol, there is a continuing need to identify additional phenol alkylation process procedures, conditions and catalysts which can be used to para-selectively synthesize desirable isopropylphenolic compounds. Accordingly, it is an object of the present invention to provide a process for alkylating phenol to produce a product mixture enriched in the para-isomer of isopropylated phenolic materials.